DESCRIPTION (Verbatim from the Applicant's Abstract): The hippocampus is an important cognitive brain region by virtue of its critical role in learning and memory. In the adult hippocampus of the female rat, the CA3-CA1 synapses undergo phasic cycles of syanptogenesis and synapse shedding with each 4 or 5 day estrous cycle. Although this cycle requires the ovarian steroid estrogen, the excitatory pyramidal neurons in CA1 and CA3 lack the conventional, genomic estrogen receptor (ER alpha). This remarkable observation leads to many, unanswered questions about the control of ovarian steroid-dependent cycle of adult synaptogenesis in the hippocampus. It also begs us to ask whether this same cycle also occurs in cerebral cortex. Using the molecular biological techniques of PCR, Northern and Southern blots, and differential display, we will uncover a set of molecules that are selectively synthesized in an estradiol-dependent manner in hippocampal CA1 and CA3. The time course of selective synthesis will enable us to define a temporal cascade of expressed sequences from early time points, those presumably controlling transcription factors, through later ones, possibly including sequences involved in synapse assembly. By pharmacologically blocking estradiol-dependent synapse formation with an NMDA receptor antagonist, and independently, by hormonally undoing synapses already formed, we will identify a particularly interesting subset of these expressed transcripts. This selective subset will include estradiol-dependent transcripts specific to the synaptogenetic cascade. Interpreting the roles played by the estradiol-dependent transcripts will be facilitated by electrophysiological correlations, anatomical localization, and by structural similarities to known molecules. Using naturally cycling females and ovariectomized animals receiving estradiol replacement, we will electrophysiologically assess NMDA receptor function in CA1 and correlate this with altered gene expression. In situ hybridization, supplemented as necessary with microdissection, will permit the cellular localization of these novel gene products to pyramidal and/or nonpyramidal neurons and/or glia. In situ hybridization will subsequently be used 1) to search for similar expression patterns in cerebral cortex and hypothalamus, and 2) to compare this form of adult synaptogenesis with that in the developmentally immature, male rat. Finally, we begin a series of experiments, including cloning and mapping the newly discovered genes to mouse and human chromosomes. These studies will eventually culminate in testing the function of these novel gene products in the genetically altered mouse.